1. Field of the Invention
The present invention relates to vacuum pumps in general, and vacuum pumps operated by piezoelectric elements in particular.
2. Background Information
It is often desirable to secure various objects to other object through application of a vacuum. Typically, such a vacuum attachment of objects is accomplished by mating a surface area of the object to be secured to a corresponding surface of the other object. A vacuum is then applied to a recessed area or volume that is formed in one (or both) of the objects, creating a pressure differential that forces the objects together at the mating surfaces.
In most applications, vacuum attachment is used for only a short duration. For example, vacuum devices are often employed in pick and place machines, and for moving objects such as windshields during manufacturing operations. In general, vacuum attachment is not suitable for long-term purposes because the vacuum will decrease over time due to leakage. Oftentimes, a pliable material, such as rubber is used at the mating surfaces to form a seal, thereby enhancing the level of vacuum that may be obtained. Unfortunately, these materials allow gases to slowly pass through them, resulting in the loss of vacuum over time.
One way to combat the loss of vacuum over time is to employ a vacuum pump to replenish the level of vacuum on at least an intermittent basis. However, conventional vacuum pumps are both noisy and have limited lifetimes. Furthermore, the vibrations they cause generally make them unsuitable for high-precision applications.
Accordingly, there is a need for a vacuum apparatus that may be employed to maintain a vacuum for sustained periods of time. Ideally, such an apparatus should be extremely reliable, and produce virtually no noise or vibrations.
The present invention addresses the limitations discussed above by providing a piezoelectric vacuum pump that is extremely reliable and free of vibration. The piezoelectric vacuum pump includes a diaphragm comprising an upper diaphragm member and a lower diaphragm member. The diaphragm members preferably comprise thin metal sheets that are plated with a noble metal, such as gold, silver, or platinum, and are mated together so as to form a hermetic seal along the length of the diaphragm. The piezoelectric vacuum pump further includes a plurality of piezoelectric bimorph elements that are mounted to the upper surface of the upper diaphragm member. When the piezoelectric bimorph elements are electrically activated, they cause a localized portion of the upper diaphragm member to flex, thereby creating a change in volume in a portion of the diaphragm proximate to that piezoelectric bimorph element. The apparatus further includes a sequencing circuit that provides a patterned switching sequence to control electrical activation of selected piezoelectric bimorph elements such that a volume of gas is drawn into an input port, moved through the diaphragm, and exhausted out of an output port.
In one embodiment, the piezoelectric vacuum pump is designed so that it may be manufactured using conventional printed circuit board manufacturing techniques. This enables the vacuum pump to be manufactured at a reduced cost. Furthermore, due to the extremely low failure rate characteristics of the piezoelectric bimorph elements and solid-state control electronics, the vacuum pump is extremely reliable. In addition, since the piezoelectric bimorph elements are the only moving parts and are only slightly deflected during operation, the vacuum pump virtually noiseless and vibration free.